Vehicle powertrain torsionals, i.e., Nth-order components of vehicle powertrain vibrations, may, under some operating conditions, achieve undesirably high magnitudes, and the occurrence of such high magnitude torsionals over an extended duration may result in potential vehicle powertrain or drivetrain damage. It is desirable to diagnose and/or control such torsionals to determine the frequency of their occurrence and/or to control powertrain operation away from conditions at which they occur.